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The present invention discloses a method and a device for preparing a
compound semiconductor film. The method comprises the steps of: providing
a substrate above at least an evaporation source in a vacuum condition;
heating a source material contained in the evaporation source so that the
source material is vapor-deposited on the substrate; and taking out the
substrate under protection of an inert gas. The substrate may be rotated
around an axis of a plane where the evaporation source is positioned, and
the substrate is tilted by a predetermined angle with respect to the
plane. The compound semi-conductive film thus prepared has a uniform
thickness with a larger area. The method provides a simplified process
and enhanced efficiency.

20. A method for preparing a compound semiconductor film, comprising:
providing at least one source material in an evacuated container;
providing a substrate in the container, wherein the substrate is disposed
above the source material, and wherein the substrate forms an angle of 5
to 30 degrees with respect to a horizontal plane; rotating the substrate;
evaporating the source material; depositing the source material on the
substrate while it is being rotated to provide a compound semiconductor
film on the substrate; and applying an inert gas.

21. The method of claim 20, wherein the angle is 7 to 8 degrees.

22. The method of claim 20, wherein rotating is at a speed of 3-100
r/min.

23. The method of claim 20, wherein at least two source materials are
provided; wherein the source materials are placed on the same plane; and
wherein the source materials are evenly distributed around a circle on
the plane.

24. The method of claim 23, wherein the substrate has a square shape, and
wherein the circle has a radius 8-10 times of the side length of the
substrate.

25. The method of claim 24, wherein the substrate has a geometric center
aligned with the center of the circle on a same vertical line to the
plane; and wherein the substrate is rotating around the geometric center.

26. The method of claim 20, wherein a plurality of substrates are
provided.

27. The method of claim 20, wherein the source material is deposited on
the substrate at a speed of about 0.3-16 nm/minute.

28. The method of claim 20, wherein the source material is
vapor-deposited on the substrate for about 30-60 minutes.

29. The method of claim 20, wherein the substrate has a temperature of
about 300-600.degree. C. during vapor-depositing.

30. The method of claim 20, further comprising: cleaning the substrate.

31. The method of claim 20, further comprising: heating the deposited
substrate for a predetermined time.

34. The method of claim 20, wherein the substrate is glass coated with a
layer of Mo.

35. A device for preparing a compound semiconductor film, comprising: a
container having an upper portion and a bottom plate; and a supporting
member disposed in the upper portion of the casing, wherein the
supporting member has a slanted surface so that a substrate disposed on
the surface of the supporting member forms an angle of 5 to 30 degrees
with respect to the bottom plate, and wherein the supporting member is
rotatable around its geometric center.

36. The device of claim 35, further comprising a vacuumizing unit for
vacuumizing the container.

37. The device of claim 35, further comprising a gas supply for providing
an inert gas into the container.

38. The device of claim 35, wherein the thickness of the supporting
member tapers from the edge of the supporting member to the center of the
supporting member, so that the supporting member has a slanted surface to
support the substrate.

39. The device of claim 35, wherein the slanted surface forms an angle of
7-8 degrees with respect to the bottom plate.

Description

CROSS REFERENCE RELATED APPLICATION

[0001] This application claims priority to Chinese Patent Application No.
200910106258.9, filed to SIPO on Mar. 31, 2009, the entirety of which is
hereby incorporated by reference.

TECHNICAL FIELD 0F THE INVENTION

[0002] The present invention relates to the field of solar battery, more
particularly to a method and a device for preparing a compound
semiconductor film respectively.

BACKGROUND 0F THE INVENTION

[0003] Solar batteries of compounded semiconductor film series are one of
the most efficient and potential ones in thin-film solar batteries.
Compound semiconductor material has the highest light absorption
coefficient in known semiconductor materials, which may reach up to
10.sup.5/cm, without semiconductors having S-W effect (Staebler-Wronski
Effect). Moreover, converting efficiency thereof may be enhanced by light
irradiation. Therefore, this kind of solar batteries may have a long
lifespan. It is shown by experiments that compound semiconductor film
solar batteries have even longer life span than monocrystalline silicon
batteries which may last for normally 40 years. And the compound
semiconductor is a direct band gap semiconductor material, which is most
suitable for film.

[0004] Currently, there are many methods for preparing a compound
semiconductor film. To overcome disadvantages of the method in the prior
art, a vacuum evaporating method was brought forward.

[0005] The vacuum evaporating method means that source material is heated
in an evaporation container in the vacuum conditions so that atoms or
molecules are evaporated or escaped from the surface and form a steam
flow incident onto the surface of the substrate and then condense into a
solid thin film. The compound semiconductor thin film solar battery
prepared thereof may have high converting efficiency. However, the
battery area prepared is far less than 1 cm.sup.2, which is mainly
limited by emitting characteristics of the evaporation source. While
preparing thin film with a large area, the coating material distribution
is severely uneven. The larger the scale is, the more uneven the material
distribution is. Due to the large area requirement to the solar battery,
this method does not have industrial commercialbility.

[0006] To improve the method, line movement of the substrate is suggested,
with rod-shaped evaporation source for vapor depositing the coating film.
Although semiconductor film with relatively large area may be achieved in
this case, the uniformity thereof is still low, normally around .+-.10%.
However, the rod-shaped evaporation source is hard to prepare, because
the rod-shaped source shall have the same temperature in each part
thereof for uniform evaporation. And there shall have no slower or faster
evaporation parts existing herein. However, even the internal defect
distribution inside the evaporation source may affect the evaporating
speed or cause slower or faster evaporation at certain parts. Therefore,
it is very complex for theoretical calculation to the rod-shaped
evaporation source which is hard for processing. Further, the whole
apparatus is expensive and need precise control.

SUMMARY OF THE INVENTION

[0007] In viewing thereof, the present invention is directed to solve at
least one of the problems existing in the prior art. Accordingly, a
method for preparing a compound semiconductor film is provided, in which
the difficulty in manufacturing the evaporation source and the film
unevenness may be overcome accordingly.

[0008] Further, a device for preparing a compound semiconductor film may
also need to be provided accordingly.

[0009] According to an embodiment of the invention, a method for forming a
compound semiconductor film may be provided, which may comprise the steps
of: providing a substrate above at least an evaporation source in a
vacuum condition; heating source material contained in the evaporation
source so that the source material may be vapor deposited on the
substrate; and taking out the substrate under protection of inert gas.
The substrate may be rotated around an axis that may be normal to a plane
where the evaporation source may be positioned, and the substrate may be
tilted by a predetermined angle with respect to the plane.

[0010] According to another embodiment of the invention, a device for
forming a compound semiconductor film on a substrate may be provided,
comprising: a casing; a vacuumizing unit for vacuumizing the casing; at
least an evaporation source provided in the casing; and a supporting
member provided above the at least an evaporation for supporting at least
a substrate for forming the compound semiconductor film thereon. The
supporting member may be formed with a slanted surface where the at least
a substrate is provided.

[0011] The compound semi-conductive film prepared according to the method
in the present invention has a uniform thickness with larger area.
Further, the process is relatively simple, efficient and also easy to
realize. Meanwhile, the present invention can be realized by directly
modifying the prior evaporation device, and also the modification is easy
and investment is low. And it realized large scale substrate by a smaller
device, so in practical production, it is more applicable.

[0012] Additional aspects and advantages of the embodiments of present
invention will be given in part in the following descriptions, become
apparent in part from the following descriptions, or be learned from the
practice of the embodiments present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] These and other aspects and advantages of the invention will become
apparent and more readily appreciated from the following descriptions
taken in conjunction with the drawings in which:

[0014] FIG. 1 shows a substrate divided into nine parts according to an
embodiment of the invention;

[0015] FIG. 2 shows a schematic view of a device for preparing a compound
conductor film according to an embodiment of the invention;

[0016] FIG. 3 shows a plan view of a supporting member for supporting
substrates according to an embodiment of the invention; and

[0017] FIG. 4 shows a plan view of the distribution of evaporation sources
according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

[0018] Reference will be made in detail to embodiments of the present
invention. The embodiments described herein with reference to drawings
are explanatory, illustrative, and used to generally understand the
present invention. The embodiments shall not be construed to limit the
present invention. The same or similar elements and the elements having
same or similar functions are denoted by like reference numerals
throughout the descriptions.

[0019] According to an embodiment of the invention, a method for forming a
compound semiconductor film on a substrate may be provided, comprising
the steps of: providing a substrate above at least an evaporation source
in a vacuum condition; heating source material contained in the
evaporation source so that the source material may be vapor deposited on
the substrate. The substrate may be rotated around an axis that may be
normal to a plane where the evaporation source may be positioned, and the
substrate may be tilted by a predetermined angle with respect to the
plane.

[0020] The compound semiconductor film may be those known in the art, for
example a CIS thin film, a CIGS thin film, a CuInS.sub.2 thin film, a
CIGSS thin film, a CdS thin film, a CdTe thin film and so on.

[0021] According to an embodiment of the present invention, the vacuum
degree is less than 3.0.times.10.sup.-3 Pa in the vacuum condition.
Further, an evaporation system for implementing the method may be heated
to enhance the vacuum degree.

[0022] Normally, source material, such as powdered pure metal substance or
alloy thereof, may be selected for preparing the required compound
semiconductor thin film, for example Cu, In, Ga and Se, or CuSe alloy,
InSe alloy and GaSe alloy. Further, CuInGaSe alloy may be directly
adopted to prepare the CuInGaSe semiconductor thin film. For preparing a
CdTe semiconductor thin film, Cd powder and Te powder may be used, or
CdTe powder may as well be used accordingly.

[0023] The evaporation source may be that normally known in the art, which
will not be described herein for simplicity purpose. An evaporation
source may have a blocking plate to be opened during evaporation
depositing which is then closed after evaporation depositing. For
example, the evaporation source may be a heating evaporation container,
after placing the above source material therein, the source material will
be heated and vaporized accordingly. Normally, the evaporation source may
be divided into a resistance evaporation source, an electronics beam
evaporation source, a high frequency inducing evaporation source, a laser
beam evaporation source and so on.

[0024] The substrate may normally have a square shape made from any kind
of glasses or flexible substrate prepared from macromolecular organics.
According to an embodiment of the present invention, the substrate may be
a NaCa glass which is magnetron sputtered with a layer of Mo electrode
substrate having a thickness of 1 .mu.m.

[0025] The substrate may be ultrasonically cleaned to ensure cleanness of
the substrate.

[0026] There may be one or more evaporation sources according to selection
of the source material. For example, for a CuInGaSe film, if the CuInGaSe
source material is adopted, only an evaporation source may be selected.
However, when Cu, In, Ga and Se are adopted as the source materials, four
evaporation sources, i.e., a Cu evaporation source, an In evaporation
source, a Ga evaporation source and a Se evaporation source, may be
adopted accordingly.

[0027] The vapor depositing is commonly practiced in the art, and the
detailed description thereof is omitted hereby for clarity purpose.

[0028] Further, the detailed steps of the present invention will be
described as follows:

[0029] Firstly, the substrate may be fixed in a slanting or tilted manner
over the evaporation source after ultrasonic cleaning. And the source
material may be deposited into each evaporation source. Then it is
vacuumized, and the substrate is heated up to 300-600.degree. C. and the
temperature is maintained to heat the evaporation source and adjust a
vapor depositing speed of each evaporation source gradually. And the
rotating speed of the substrate may be adjusted. Then, the evaporation
depositing may be started. After evaporation depositing, the substrate
may be continuously heated for a predetermined period of time so that the
compound semiconductor thin film may react more thoroughly. Then, the
substrate may be naturally cooled to normal temperature, and the
substrate is under the protection of inert gas by slowly filling
protection gas. When the pressure may reach atmosphere pressure, the
substrate is taken out, and the substrate deposited with a compound
semiconductor thin film is provided accordingly.

[0030] According to an embodiment of the present invention, the rotating
speed of the substrate may be 3-100 r/min.

[0031] According to an embodiment of the present invention, the substrate
may be tilted by 5-30 degrees with respect to the plane. According to
another embodiment of the present invention, the substrate may be tilted
by 7-8 degrees with respect to the plane accordingly. It should be noted
that the angle between the substrate and the plane in the present
invention means the acute angle.

[0032] If a plurality of evaporation sources, for example 2 or 4
evaporation sources, are provided, evaporation sources may be evenly
distributed on a phantom circle in the plane. For example, the
evaporation sources may be located at the equal division points of the
circumference of the circle.

[0033] According to an embodiment of the present invention, a plurality of
substrates may be provided, with a geometric centre thereof being aligned
with the center of the circle on a same vertical line to the plane.

[0034] According to an embodiment of the present invention, the substrate
may have a square shape, and the circle may have a radius which may be
8-10 times of the side length of the substrate.

[0035] In this case, since the evaporation sources may uniformly
distributed, a plurality of elements, such as Cu, In etc, may be vapor
deposited at the same time during the rotation of the substrate. And
according to the distribution characteristics of the evaporation gas
flows from the evaporation sources, the substrate may be adjusted to be
tilted by a predetermined angle with respect to the plane where the
evaporation sources are located so that the thickness of the thin film on
the substrate may be compensated accordingly. Therefore, the prepared
thin film may have a better uniformity and may realize large scale
uniform depositing.

[0036] According to an embodiment of the invention, each evaporation
source may have an evaporation depositing rate of about 0.3-16 nm/min.

[0037] The protection gas may be those normally used in the art, for
example, it may be highly purified Ar or N.sub.2.

[0038] The compound semiconductor film prepared may be divided into nine
areas with the same shape by dividing the length and width of the film
into three parts respectively. The uniformity of the whole film is then
measured, with testing results showing that the thickness uniformity
thereof falls within .+-.5% whereas the thickness uniformity of the film
prepared by conventional method is about .+-.17.5%, at most .+-.10%.

[0039] The compound semiconductor film prepared in the present invention,
each element is equally distributed and it is easy to control the
composition on a film with a larger area. When element distributions on
the substrate are analyzed by EDS (Energy-Dispersive Spectrometry), the
results show that the elements are distributed evenly on each area. The
present invention is most suitable for preparing semiconductor films
which may have a stricter requirement to element distributions, such as a
CIS layer, a CIGS layer, a CuInS.sub.2 layer, a CIGSS layer, a CdS layer
and a CdTe layer of polycrystalline film solar battery and so on.

[0040] The compound semiconductor film prepared in the present invention
has excellent photoelectric performance, the prepared CIGS solar battery
with a size of 15.times.15 cm.sup.2 is tested under a light intensity of
AM 1.5. The highest battery conversion efficiency may reach 14.93% which
may have commercial potentiality.

[0041] The present invention inherits advantages of the conventional
evaporation, and may control the crystalline quality and electric
performance of the film. Meanwhile the process is simple and efficient
which is also easy for realization. Besides, the present invention may be
achieved by easily and directly modifying the original evaporation
depositing device with low cost. And the substrate with a large area,
such as 15.times.15 cm.sup.2, may be produced by miniaturized device so
that it is more applicable in practical production.

[0042] In the following, a device 100 for preparing a compound
semiconductor film will be described with reference to accompanying
figures.

[0043] As shown in FIG. 2, according to an embodiment of the invention,
the device 100 may comprise: a casing 101; a vacuumizing unit 102 for
vacuumizing the casing 101; at least an evaporation source 104 provided
in the casing 101; and a supporting member 105 provided above the at
least an evaporation source 104 for supporting at least a substrate 106,
such as a glass substrate, for forming the compound semiconductor film
thereon. The supporting member 105 may be formed with a slanted surface
107 where the at least a substrate is provided. According to an
embodiment of the invention, the device 100 may further comprise a gas
supply for supplying inert gas into the casing. The supporting member 105
may be formed into a bracket configured to support the at least a
substrate 106. Further, the evaporation source 104 may have a blocking
cover 108 which is closed when it is not working. And the blocking cover
108 is opened when evaporating deposition is started. There is an
evaporation distance L between the substrates 106 for forming the
compound semiconductor film, which may be adjusted according to
evaporating deposition requirements. According to an embodiment of the
invention, the slanted surface 107 may be tilted by an angle .theta. of
about 5-30 degrees with respect to the bottom surface. According to an
embodiment of the invention, the slanted surface 107 may be tilted by 7-8
degrees with respect to the bottom surface.

[0044] As shown in FIG. 3, the supporting member 105 may be rotatable
around an axis 3 thereof, the axis 3 is the geometric center of the
supporting member. And the rotating speed thereof may be controlled to
substantially 3-100 r/min. It should be noted that the supporting member
105 is configured to have a relative rotational movement with respect to
the at least an evaporation source 108 during operation. For example,
according to an embodiment of the invention, the supporting member 105
may be stationary, and the evaporation source 108 may be rotatable with
respect to the supporting member 105. According to another embodiment of
the invention, the supporting member 105 and the evaporation source 108
may be rotatable respectively. However, the rotating speed of the
supporting member 105 is different from that of the evaporation source
108, so that there is a relative rotational movement between the
supporting member 105 and the evaporation source 108.

[0045] As shown in FIG. 3, the substrate 106 may have a square shape. And
there may be a plurality of substrates 106 provided on the supporting
member 105. It should be noted that there is no limitation to the shape
of the substrate, only if the substrate should meet industrial
requirement. Thus, the shape illustrated here is just for description
rather than limitation.

[0046] As shown in FIG. 4, a plurality of evaporation sources 104 may be
provided on a bottom surface of the casing 101. And at least two
evaporation sources 104 may be evenly distributed on a phantom circle 2
in the bottom surface. The circle 2 may have a radius which may be about
8-10 times of a side length of the substrate 106. According to an
embodiment of the invention, 2 or 4 evaporation sources 104 may be
distributed evenly on the bottom surface of the casing 101.

[0047] The present invention will be further explained in conjunction with
detailed examples.

First Embodiment

[0048] (1) The substrate after ultrasonic cleaning is fixed by, for
example, a substrate clamp and the angle between the substrate and the
plane is 8 degrees. The substrate has an area of 15.times.15 cm.sup.2 and
it is a NaCa glass which is magnetron sputtered by a layer of Mo
electrode substrate having a thickness of 1 .mu.m.

[0049] (2) Evaporation sources with Cu, In, Ga and Se are uniformly fixed
in a phantom circle at the four quartering points respectively. The
circle has a radius of 9 times of the side length of the substrate.

[0050] (3) Then, it is vacuumized by the vacuumizing unit 102 to
3.0.times.10.sup.-3 Pa and the device 100 for implementing the method of
the invention is heated to further remove gas contained herein until the
vacuum degree reaches up to 2.0.times.10.sup.-4 Pa. Meanwhile the
substrate is heated up to 500.degree. C., then the temperature is
maintained thereafter.

[0051] (4) The evaporation speed of each evaporation source may be
adjusted. The evaporation speed of the Cu evaporation source is about 15
nm/min. The evaporation speed of the In evaporation source is about 12
nm/min; The evaporation speed of the Ga evaporation source is about 7
nm/min; and the evaporation speed of Se evaporation source is about 35
nm/min.

[0052] (5) The substrate may have a rotating speed of about 5 rad/min.
Normally, evaporation depositing may be started for about 50 minutes
after parameters thereof having been preset with the blocking plate of
each evaporation source being removed. After the evaporation depositing,
the blocking plate is closed. Then, the substrate is heated for 3
minutes, and the substrate is cooled to room temperature in the ambient
environment thereafter.

[0053] (6) Finally, the vacuumizing system for vacuum pumping is closed
with highly purified N.sub.2 being slowly injected into the accommodating
cavity until an internal pressure thereof may reach atmospherical
pressure. Then, the substrate may be taken out with the desired film
being formed thereon. The substrate is denominated as A1.

Second Embodiment

[0054] Compared with First Embodiment, the only difference may lie in that
the angle between the substrate and the plane is 5 degree. The radius of
the circle is about 8 times of the side length of the substrate. And the
rotating speed of the substrate is about 20 rad/min, the remaining
features thereof is the same as First Embodiment, and the substrate may
be denominated as A2.

Third Embodiment

[0055] Compared with First Embodiment, the only difference may lie in that
the angle between the substrate and the plane is 30 degree. The radius of
the circle is ten times of the side length of the substrate. The rotating
speed of the substrate is about 90 rad/min, the remaining features are
the same as First Embodiment, and the substrate may be denominated as A3.

Fourth Embodiment

[0056] The Fourth Embodiment is substantially the same as First
Embodiment, with the only difference lying in that the substrate is
replaced by a substrate with a CdS layer being formed by Chemical Bath
Deposition (CBD deposition). Besides, the evaporation source materials
are replaced by metals Cd and Te with the evaporation speed being
adjusted to 32 nm/min and 47 nm/min respectively. And the rotating speed
thereof is about 90 rad/min with the evaporation time being 33 minutes.
The remaining features are the same as those in First Embodiment. The
substrate may be denominated as A4.

Fifth Embodiment

[0057] Compared with Fourth Embodiment, the only difference may lie in
that the rotating speed of the substrate is adjusted to 5 rad/min with a
tilting angle of the substrate being about 30 degrees. The remaining
features are substantially the same as those in Fourth Embodiment. The
substrate may be denominated as A5.

First Comparative Embodiment

[0058] The only difference with First Embodiment may lie in that the
substrate is placed in parallel with the plane rather than tilted. The
remaining features are the same as those in First Embodiment. The finally
obtained substrate in this comparative embodiment may be denominated as
D1.

Second Comparative Embodiment

[0059] The only difference with First Embodiment may lie in that the
substrate is tilted by 35 degrees with respect to the plane, with the
remaining features being substantially the same as those in the First
Embodiment. The finally obtained substrate in this comparative embodiment
may be denominated as D2.

Third Comparative Embodiment

[0060] The only difference with the Fourth Embodiment may lie in that the
substrate is tilted by 35 degrees with respect to the plane. The
remaining features are substantially the same as the Fourth Embodiment.
And the substrate is denominated as D3.

[0061] Performance Test

[0062] Uniformity of Film Thickness

[0063] Films A1-A5 and films D1-D3 are divided into nine areas according
to FIG. 1. The film thickness in each area is tested by a step profiler,
such as a Xp-2 step profiler normally practiced in the art. The thickness
is denominated as x.sub.1, x.sub.2, x.sub.3, x.sub.4, x.sub.5, x.sub.6,
x.sub.7, x.sub.8, and x.sub.9 respectively. The average value of x.sub.1,
x.sub.2, x.sub.3, x.sub.4, x.sub.5, x.sub.6, x.sub.7, x.sub.8, and
x.sub.9 is denominated as x.sub.0. In the present invention, the maximum
value and the minimum value of (x.sub.i-x.sub.0)/x.sub.0 (i=1.about.9)
are used to evaluate the uniformity of the film thickness.

[0064] Light Conversion Efficiency

[0065] The light conversion efficiency is calculated by measuring J-V
characteristics of a battery. The testing of the J-V characteristic of
the battery is performed under a sun light simulator with a light
intensity of AM1.5 in a laboratory, and a xenon lamp is adopted as the
light source. The light intensity of the simulator is calibrated by a
monocrystalline Si standard battery provided by 205 metering station, the
18th Electronic Research Institute, Tianjin. And the output power of the
light source in the simulator is adjusted so that the short circuit
current may reach a calibration value with a battery testing temperature
of 25.degree. C.

[0066] Uniformity of Chemical Content in Film

[0067] The films A1-A5 and D1-D3 are divided into nine areas according to
FIG. 1. And the atomic ratio in each area is tested by a QUEST X-Ray
spectrometer distributed by NORAN Inc., United States of America. The
atomic ratio is denominated as y.sub.1, y.sub.2, y.sub.3, y.sub.4,
y.sub.5, y.sub.6, y.sub.7, y.sub.8 and y.sub.9 respectively. The average
of y.sub.1, y.sub.2, y.sub.3, y.sub.4, y.sub.5, y.sub.6, y.sub.7, y.sub.8
and y.sub.9 may be denominated as y.sub.0. The maximum value and the
minimum value of (y.sub.i-y.sub.0)/y.sub.0 (i=1.about.9) are used to
evaluate the uniformity of the film thickness.

[0068] From table 1, it can be concluded that the uniformity of the film
thickness has been enhanced tremendously during the preparation of the
CuInGaSn film. And the light conversion efficiency is enhanced to a great
extent.

[0069] From table 2, it can be concluded that the uniformity of the film
thickness has been enhanced obviously during the preparation of the CdS
film. And the uniformity of the chemical content is enhanced to a large
extent.

[0070] Although explanatory embodiments have been shown and described, it
would be appreciated by those skilled in the art that changes,
alternatives, and modifications can be made in the embodiments without
departing from spirit and principles of the invention. Such changes,
alternatives, and modifications all fall into the scope of the claims and
their equivalents.